The present invention relates to an automatic drain device to discharge liquid accumulating in a high pressure air tank of an air compressor.
Typical applications for an air compressor supplying high-pressure air, generally around 7 kg/cm.sup.2, are a high-pressure air drill, a tacking instrument, a rock drill, a punching machine, an air hammer, an air turbine, and the like. In applications of this type, the air compressor usually stores a reserve of the high-pressure air in an air tank to minimize fluctuations of output air pressure.
Oil and water that separates from the compressed air collects at the bottom of the air tank as liquid that must be removed periodically during operation.
Air compressors incorporating automatic liquid discharge capability are well known. According to prior art, these drain devices use a float chamber and a drain valve in a drain pipe path below the air tank, and a controller to automatically open the drain valve to drain liquid that gravitates from the air tank into the float chamber. A mechanically actuated float level switch within the float chamber sends a signal to a time-constant circuit in the controller when the liquid inside the float chamber reaches a certain level. Upon receiving this signal, the time-constant circuit activates a valve drive circuit, which in turn opens the drain valve for a preset period to drain the liquid in the float chamber. At the end of the preset period the energizing signal to the valve drive circuit is removed and the drain valve closes. This sequence is repeated each time the liquid level in the float chamber rises sufficiently to activate the float level switch.
Problems that may be encountered in an automatic drain device using the prior art are:
(1) The float chamber must be large enough to accommodate a mechanically actuated float level switch that is responsive to liquids, including oil, which have high viscosity. This increases the size of the air compressor system.
(2) The float level switch usually consists of a float and a switch connected by a mechanical part, such as a lever, which may become corroded by the liquid in the float chamber.
(3) The variability of the viscosity of the liquid in the float chamber can affect the reliability of the float to always detect the same level of liquid in the chamber. This can be particularly troublesome in cold environments where the viscosity of the liquid increases. Accumulation of residue in the float chamber may also affect the reliability of the float level switch.
The questionable reliability of automatic drain devices using the prior art increases the possibility of liquid remaining in the air tank and the consequent difficulty in continuously supplying clean, high pressure air from the air compressor system.